Exam 1 Flashcards
How do stars appear to rise and set?
Stars first rise near the eastern horizon, move upward and toward the south, and then move down and set near the western horizon.
How does latitude affect our what we see in our local sky?
It affects the locations of the horizon and zenith relative to the celestial sphere.
Galaxy
A great island of stars in space, containing from a few hundred million to a trillion or more stars, all held together by gravity and orbiting a common center.
Stars are grouped into what?
Constellations
Zenith
Point directly overhead.
Partial eclipse
Occurs if you are on the Earth that does not get completely covered by the Moon’s shadow.
Rotation
The spinning of an object around it axis.
Orbit (revolution)
The orbital motion of one object around another due to gravity.
Arcminute
Each degree has 60 arcminutes.
Declination
Position above or below the celestial equator.
What phase follows the waxing gibbous? And which direction of the moon is illuminated?
Full moon. Entire surface visible to earth is illuminated.
What is the dark side of the moon?
The side of the moon not lit by the sun.
Angular distance
Between objects in the sky is the angle that appears to separate them.
The moon’s shadow falls on the earth during a ___ eclipse.
Solar
Cluster (group) of galaxies
A collection of galaxies bound together by gravity. Small collections are called groups, while larger ones are called clusters.
Solar system
The sun and all the material that orbits it, including planets, dwarf planets, and small solar system objects.
Earthshine
Reflected sunlight from earth’s surface to the moon. It’s real!
The moon returns to the same position (relative to the sun) every?
29.5 days (This is because, as the Moon is orbiting the Earth, the Earth is orbiting the Sun, so when the Moon completes one 27.3 day orbit, it has to go a little extra to catch up to where the Sun is in our sky.)
Is the dark side and far side of the moon the same thing?
No. There will always be a “far side” from earth but the moon is lit just as the earth is so there is only the perceived “dark side” from earth.
What phase follows the first quarter? And which direction of the moon is illuminated?
Waxing (growing) gibbous. Ride side illuminated.
When the earth is directly between the sun and moon we have a ___ eclipse.
Lunar
Lunar eclipses can only happen during the phase of the moon called ___.
Full moon. Because the earth must cast its shadow on the moon.
Comet
A relatively small and ice-rich object that orbits a star.
Star
A large glowing ball of gas that generates heat and light through nuclear fusion in its core
Asteroid
A relatively small and rocky object that orbits a star.
Local sky
The sky seen as from wherever you are.
How do you pinpoint an object in the sky?
Stating its direction along the horizon and its altitude above the horizon.
The amount of the moon we see illuminated changes. This is called what?
Phases
Solar eclipses can only happen during the phase of the moon called ___.
New moon. Because the moon must cast its shadow on earth.
Moon (Satellite)
An object that orbits a planet.
What phase follows the waning gibbous? And which direction of the moon is illuminated?
Third quarter. Left side is illuminated.
Does the moon go completely dark during an eclipse? Why or why not?
No, it turns reddish. Because of earthshine.
After the new moon, we see what phase next? And which direction of the moon is illuminated?
Waxing (growing) crescent. Only the right side of the moon is illuminated.
Right ascension
Position along the celestial equator.
What phase follows the full moon? And which direction of the moon is illuminated?
Waning gibbous. Left side is illuminated.
Expansion
The increase in the average distance between galaxies as time progresses.
Horizon
The boundary between earth and sky.
Celestial sphere
What the ancients believed. Since we lack depth perception, the stars seem to lie on the same plane when in fact they are very far apart.
Astronomical unit
AU. The average distance between earth and the sun; about 150 million kilometers.
What phase follows the waning crescent? And which direction of the moon is illuminated?
New moon. No visible illumination.
Light year
Distance, not time. Distance it takes light to travel in one year; about 9.46 trillion kilometers.
Meridian
An imaginary half circle stretching from the horizon due south, through the zenith, to the horizon due north.
What is the far side of the moon?
The side opposite earth’s view.
What is the cause of retrograde motion?
We see something in retrograde motion when we pass it in its orbit. Like when earth passes mars, it appears to move backwards.
Does the tilt of the earth change as it orbits?
No
The moon orbits earth every?
27.3 days
Synchronous rotation
Describes how the Moon rotates exactly once with each orbit.
Are the celestial poles and equator real lines?
No, they are imagined points in space.
Why is the celestial sphere helpful?
It allows us to map the sky as seen from earth.
Why don’t we have an eclipse every month?
If the Moon’s orbital plane was exactly aligned with the ecliptic, we should have a solar eclipse every new moon, and a lunar eclipse every full moon. ✤ However, the Moon’s orbital plane is off the ecliptic by 5 degrees. ✤ To have an eclipse, the new or full moon has to occur at one of the nodes of the Moon’s orbit - the point where the orbit crosses the ecliptic.
Small solar system body
An asteroid, comet, or other object that orbits a star but is too small to qualify as a planet or dwarf planet.
South celestial pole
The point directly over the earth’s south pole.
When we can’t see the moon during a normal month because it rises with the sun it’s called what?
New moon
Annular eclipse
Occurs when the moon is at a farther point in its orbit so its angular size is not large enough to entirely block out the sun.
Is the earth the same distance from the sun all year?
No. Distance from the sun is not why we have seasons. If it were, we’d have the same season al year.
North celestial pole
The point directly over the earth’s north pole.
Eclpiptic
The path the sun follows as it appears to circle around the celestial sphere once each year.
Are seasonal changes more extreme at high latitudes?
Yes!
What does tidally locked mean?
We see the same side of the moon all the time.
Arcsecond
Each arcminute has 60 arcseconds.
Universe (cosmos)
The sum total of all matter and energy - that is, all galaxies and everything between them.
What phase follows the third quarter? And which direction of the moon is illuminated?
Waning crescent. Left side illuminated.
Local motion
•Sun and nearby stars move at random with respect to one another. •We move relative to other stars around 70,000 km/hr. •Constellations will change over long periods.
Our cosmic address
The local group. Milky Way, Andromeda, and several other small galaxies. Austin Texas USA The Earth The Solar System The Milky Way Galaxy The Local Group of Galaxies The Local Supercluster of Galaxies The Universe
Supercluster
A gigantic region of space in which many groups and clusters of galaxies are packed more closely together than elsewhere in the universe.
When the moon is directly between the sun and earth we have a ___ eclipse.
Solar
How much of the moon is illuminated by the sun at any one time?
Half. Although from earth we may not be able to see.
Why couldn’t the ancients understand retrograde motion?
Because they assumed the stars and planets were aligned in the celestial sphere.
The earth’s shadow falls on the moon during a ___ eclipse.
Lunar
Planet
A moderately large object that orbits a star and shines primarily by reflecting light from its star.
What phase follows the waxing crescent? And which direction of the moon is illuminated?
First quarter. Right side again is illuminated.
Star system
A star (sometimes more than one) and any planets and other materials that orbit it.
Celestial equator
A projection of earth’s equator into space, makes a complete circle around the celestial sphere.
Observable universe
The portion of the entire universe that can be seen from earth, at least in principle. (probably just a tiny portion of what’s out there)
Angular size
The angle an object appears to span in your field of view.
Why do we have seasons?
The tilt of the earth towards the sun, yes. But also because summer months mean more direct sunlight for longer periods of time.
